Top up benefits ...working 3hrs

Hi karenslack21 - one of the really good things about ESA is the idea that you can do some work while you are technically too ill to work. This is called 'permitted work', and if the DWP are ok with you doing 'permitted work' then you can work up to 16 hours a week, earn up to £120 a week, and all your permitted work earnings will be disregarded for all means tested benefits, including housing benefit. There is a form and further explanation of the rules on the DWP website: https://www.gov.uk/government/publications/employment-and-support-allowance-permitted-work-form
There are also some issues to be aware of when contemplating permitted work, and the major one is that sometimes DWP may re-evaluate your 'limited capability for work' status if they think that your condition may have improved since your last work capability assessment. Also, the next time you have a WCA, they will consider the fact that you are doing permitted work. The key here is to make sure you continue to satisfy all the activities, descriptors and points which got you ESA in the first place, and make sure you emphasise that your condition has not changed for the better. It's also important to be aware of the exact points you got for each activity and ensure that the work you are doing does not suggest that you could no longer score these points. An example could be if someone was getting ESA because of their walking limitations - if their permitted work job meant that they had to walk a lot, then DWP might question things. This is not to put you off at all, but just to advise you to be careful. Any permitted work needs to be done on a relatively casual basis, with an employer who is fully aware of your condition. 
I hope this is helpful!

Jayne